1. Field of the Invention
The present invention relates to a testing apparatus and a testing method for testing a memory-under-test such as a semiconductor memory.
More specifically, the invention relates to a testing apparatus for conducting a writing test of the memory-under-test.
2. Related Art
Conventionally, as a semiconductor memory, there have been known a flash memory and the like. While the semiconductor memory may be used for various uses, it requires a certain data write time in accordance to its use. Here, the data write time means a time required for finishing a writing process of predetermined data in writing the data into the semiconductor memory.
A case of using such semiconductor memory for storing image data of a digital video camera will be explained below for example. In transferring data of VGA image (about 310,000 pixels) in shooting video image, its data amount per frame is about 5 Mb. The data amount per frame is reduced to 242 Kb for example by compressing the data.
When a number of frames of the video image is supposed to be 30 frame per second, a transfer time per frame is about 33 ms. However, because the data transfer time contains a time for verifying operation and the like, all of that time cannot be used for writing data. Then, 8 ms in the transfer time of each frame is appropriated to the time for writing data for example. That is, in the case described above, it is necessary to be able to write the data of 242 Kb to the semiconductor memory per 8 ms.
If a storage capacity of the semiconductor memory per page is 2 KB, 15 pages are necessary in order to store the data of one frame. Accordingly, in the case described above, the semiconductor memory is required to be able to write 15 pages in 8 ms.
There has been known a test for measuring the data writing time as described above as an item for testing a memory-under-test such as the semiconductor memory. In this test, predetermined data is written into each page of the memory-under-test to measure the write time per page.
In the conventional testing apparatus, the write time per page is specified as a testing specification. For the semiconductor memory that is required to be able to write 15 pages in 8 ms like the case described above, 8 ms/15=530 μs is specified as the write time per page.
Then, when the write time per page is larger than the specified value, a block containing that page is judged to be a defective block. The block is a unit in writing data and 15 pages is assumed to be one block for example in this case.
Writing of data into the defective block is inhibited when the defective block is packaged. The memory-under-test having such defective blocks by a certain number or more is discriminated as a defective product.
Semiconductor memories that meet with the specification required in packaging are selected through such test.
However, while the specification required in packaging demands to be able to write 15 pages in 8 ms, the conventional test demands to be able to write each page in 530 μs. The specified value in the conventional test is equal to the specification required in packaging when seen from the point of view of unit of block.
However, the write time per page of the semiconductor memory is not constant and varies per page. Therefore, the condition of the specified value required in the conventional test is harder than the specification required in packaging. That is, while the specification required in packaging demands an average write time of the pages contained in the block to be 530 μs or less for example, the conventional test demands the write time of all of the pages contained in the block to be 530 μs or less.
As a result, the conventional test ends up rejecting such a semiconductor memory that is supposed to have no problem in packaging, as a defective product. Due to that, the conventional test is dropping the production yield of semiconductor memories.
Accordingly, it is an object of the invention to provide a testing apparatus and a testing method that are capable of solving the above-mentioned problem. This object may be achieved through the combination of features described in independent claims of the invention.
Dependent claims thereof specify preferable embodiments of the invention.